PSO – Positive Shut Off


These capillary-style calibrated leaks use VTI’s proprietary Positive Shut-Off (PSO) valves to provide instant on-off operation with essentially no dead volume. This prevents gas from bursting out of the vessel when the valve is opened. The valve’s dead volume is only 0.0001 cc, which is far lower than the 1 cc or more found in other valves. The PSO-valve leaks also minimize gas depletion rates and provide longer life even at high flow-rates. Their leak-rate control element is a crimped stainless steel capillary suitable for use with all gases.

The Positive Shut-Off Calibrated Leaks can be used in a wide variety of applications, from performing verification tests to calibrating leak testing systems to controlling gas flow into process chambers and research apparatuses. These leaks are available with an integral gas reservoir and can be loaded with any gas. They are also available without a gas cylinder for use with an external gas source. Customers can operate the valve manually or with pneumatic and electrical systems. 


  • Essentially no dead volume: no pressure burst on opening
  • Low depletion rates: suitable for high flow-rate applications and use with expensive gases
  • Responsive: instant on-off operation
  • Automated: easily integrated into production systems
  • Long-lasting: valve is only open during use
  • Suitable for a wide variety of gases and gas mixtures
  • Meets ISO requirements: NIST-traceable, A2LA-accredited Calibration Certification

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